Method of polymerizing organosiloxanes



@atented Nov. 2,1943

METHOD or POLYMERIZING ORGANOSILOXANES James Franklin Hyde and OscarKenneth J channson, Corning, N. Y., asslg-nors to Corning Glass Works,Corning, N. Y., a corporation oi New York No Drawing. Application August5, 1947, Serial No. 786,460

8 Claims. (c zoo-448.2)

The present invention relates to the production of organosiloxanepolymers from relatively low molecular weight, completely condensedsiloxanes.

High molecular weight organosiloxanepolymers may be prepared from lowmolecular weight cyclic diorganosiloxanes by contacting the cyclic Ysiloxanes with an alkali metal hydroxide. By the use of this methodsiloxanes of high molecular weight may be prepared in the forms ofviscous liquids or gels. The siloxanes thus produced are of utility aspotting compounds, lubricants, hydraulic fluids, and as intermediates inthe production of siloxane fluids, greases, and elastomers. Theinitiation of the polymerization by this method is slow. Apolymerization agent which acts more rapidly to polymerize the cyclicsiloxanes would be, desirable.

An object of the present invention is to provide improved methods forthe production of high molecular weight diorganosiloxanes by therearrangement of cyclic diorgan'osiloxanes.

Other objects and advantages of the present invention will be evidentfrom the following destription.

In accordance with a preferred form of the present invention, cyclicdicrganosiloxanes are polymerized to higher molecular weight polymers byreaction thereof with an alkali metal salt of e. triorgano silanol inamount less thanone alkali metal atom per 25 silicon atoms.

The vcyclic diorganosiloxanes are siloxanes which contain a cycle ofalternate oxygen and silicon atoms and which have two organic radi-=cals linked to each silicon atom by carbon to sili con bonds. areemployed in the process hereof are those in which at least one of theorganic radicals thus attached to each silicon atom is an alkyl radicalsuch as methyl, ethyl, propyl or higher and the other radical is analkyl, aryL- alkaryl, or aralkyl radicals such as phenyl, tolyl, orbenzyl. it is preferred that the cyclic siloxanes employed here= in donot contain more than 12 silicon atoms. Mixtures of variouslysubstituted cyclic siloxanes of the indicated types may be polymerizedto produce copolymers which contain more than one type of siloxanestructural unit. A copoiymer which contains dlalkyisiloxane structuralunits in combination with alkyarylsiloxane structural units may beprepared by the polymerization of a mixture of the corresponding cyclicsiloxanes with an alkali metal salt of a triorsano sllanol.

The cyclic diorganosiloxanes which lar weight diaryisiloxanes aboveabout 20 mars per molecule do not appear to be produced.

The alkali metal salts of triorgano silanols are compounds of the typeformula RcSlOM, in which It represents organic radicals which are linkedto the silicon by carbonto silicon bonding. and M represents an alkalimetal. The organic radicals represented by R may be alkyl radicals suchas methyl, ethyl, propyL'and higher; aryl,

alkaryl, or aralkyl radicals, such as phenyl, tolyl, or benzyl; or anycombination 01 alkyl, aryl, alkaryl, or aralkyl radicals.

The alkali metal salts may be prepared by the reaction of thecorresponding triorgano alkoxy silanes; triorgano silanois, orhexaorgano disiloxones with alkali metal oxides in the presence ofwater. The alkali metal oxide and the water may be added to the reactionmixture as the alkali metal hydroxide. reaction, it is preferred to adda lower aliphatic alcohol of boiling point below that of water. By theelimination of water from the system, the desired alkali metal salts areobtained, either in the form of crystalline hydrates or as anhydroussalts, depending upon the extent of dehydration. The hydrated salts maybe dehydrated by subjecting In order to increase the rate of thehydrates to a high vacuum inthe presence of a dehydrating agent.Anhydrous salts may also be obtained by the addition cl a solvent ofboiling point greater than that of water. After the reature below thatat which destructive distillation occurs. The alkali metal salt isemployed in amount less than 1 mol of salt per 25 atoms of silicon, andpreferably in amount less than 1 .mol per 50 atoms of silicon. It hasbeen found that rearrangement of the cyclic siloxanes to form highmolecular weight polymers may be cheated by the use of less than 1 molof alkali metal salt per 8000 atoms of silicon.

The mechanism of the reaction is not completely understood though itappears that both thealkali metal and the triorgano silyl portions ofthe salt molecules enter into the structure of pendent to some extentupon the initial alkali metal salt concentration. Higher molecularweight polymers are produced by a low alkali metal saltconcentration andthe. reaction rate is approximately proportional to the alkali metalsalt concentration.

During the polymerization of cyclic slloxanes as herein described, adisproportionation may occur with the precipitation of alkali metalsiloxane salts from the reaction mixture. This disproportionation isapparently caused by the low solubility of the particular alkali metalsalts which are formed. The disproportionation results in a decrease inthe alkali metal salt concentration, a decrease in reaction rate, and anincrease in the molecular weight of the product obtained.

If desired, the polymerization of the cyclic siloxane may be terminatedby the addition of a triorgano silicon halide in amount to give ahalogen to alkali metal atomic ratio of at least one.

con halide, the alkali metal is removed from the reaction mixture as thealkali metal halide and chain terminating triorgano silyl groups areintrodueed into the polymer. v

The polymerization of the cyclic siloxanes to j high molecular weightpolymers may occur at room temperatures. However, the rate of reac-EXAMPLES Example 1 (CHmSiOK was prepared by the reaction ofhexamethyldisiloxane with potassium amide. Potassium amide was preparedby the reaction of potassium with an excess of liquid ammonia in thepresence of a trace of ferric nitrate nonahydrate. Hexamethyldisiioxanewas added slowly to the ammoniasolution of potassium amide in amount togive a silicon to potassium ratio of 2. The reaction mixture was stirredby a stream of ammonia gas. The ammonia was allowed to evaporate slowly.The reaction prod- By the reaction of the alkali metal salt in thereaction mixture with. the triorgano siliucts thus obtained weredissolved in diethyl ether and filtered through a fritted glass funnelunder dry nitrogen. The solvent and volatile products were removed bydistillation at reduced pressure.

The potassium salt of trimethyl silanol was ob-.

with stirring to octamethylcyclotetrasiloxane in.

a reaction vessel in amount to give silicon to potassium atomic ratiosof from 177-197. The temperature was maintained at temperatures between77 C. and 171 C. At the time intervals stated in the table below, asample of the reaction mixture was removed, cooled, and weighed.Sufllcient trimethyl silicon chloride in diethyl ether solution wasadded to the reaction mixture to give a chlorine to potassium ratio of2. KCl precipitated readily from the reaction mixture and was removed byfiltration. The flitrate was heated for 3 hours at a temperature 0! C.and a pressure 010.5 mm. to remove the diethyl ether, excess trimethylsilicon chloride, and the octamethylcyclotetrasiloxane which had notbeen polymerized. The-reaction sample was then cooled to 25 C. underanhydrous conditions and weighed. The per cent of cyclic siloxanepolymerized to higher molecular weight polymer was calculated from theratio of the weight of the sample after vacuum treatment to the weightof sample removed from the reaction mixture. p

The following results were obtained by this polymerization procedure:

added to octamethylcyclotetrasiloxane in reaction vessels at 100 C. inamount to give four ditferent silicon to potassium ratios. Thetemperature was maintained at 100 C. Samples oi the reaction mixtureswere taken and the per cent of the cyclic siloxane polymerizeddetermined by the method of Example 1. The following results wereobtained:

. cent Si/K ratio mm' Time aw] Poly 1.2m we 40 Example 3 (CH3)sSiOK,prepared as in Example 1, was added to octamethylcyclotetrasiloxane inreaction vessels in amount to give five difierent silicon to potassiumratios. The temperatures were maintained at the indicated values until aconstant viscosity was obtained. The. intrinsic viscosity" wasdetermined by the expression where [1;] is the limit of the expressionas 0 anproaches zero, [1 is the intrinsic viscosity, 1; is the viscosityof the polymer solution, a is the viscosity oi the solvent, and c is theconcentration of the solution in grams of polymer per 100 ml. of

solution.

The following results were obtained where in] was determined usingtoluene as a solvent:

Bi/K Ratio Temperature Time It] Example 4 (CHa)aSiOK, prepared as inExample 1, was added to three diflerent cyclic dimethylsiloxanes inreaction vessels in amount to give silicon to potassium ratios of from188 to 192. The temperature in each case was maintained at 77 C. Samplesoi the reaction mixtures were taken and the per cent of cyclic siloxanespolymerized was de-- termined as in Example 1.

1 The following results were obtained:

Percent Cyclic Used I 'lemp. Time polym' Ratio K HmBiOh 1 H lilhrs lshrs24h l( Ha)iBl [is 193 77 asseasessia Example 5 (CI-lahSiONa was preparedby the reaction of hexamethyldisiloxane with sodium amide. Sodium amidewas prepared by the reaction oi sodium with an excess of liquid ammoniain a reaction vessel in the presence of a trace of ferric nitratenonahydrate. Hexamethyldisiloxane was added slowly to the ammoniasolution of sodium amide in amount to give a silicon to sodium ratio of2. The reaction mixture was stirred bya stream of ammonia gas. Theammonia was allowed to evaporate slowly. The reaction prod acts weredissolved in dlethyl other and filtered through a fritted glass funnelunder dry nitrogen.

Bi/No Cyclic Elilorano Time CHthSlO a [ECHflsBlQylc CaHsXC :OBi ItViscosity see - v hmmple 6 (CsHslsSiONd was prepared by the reaction ofNaOH with trlphenyl silanol. A 33 per cent by weight solution oi(cinnamon in absolute methanol was added with stirring to powderedNaDI-li in a reaction vessel in amount to give a silicon to sodium ratioof 1. The methanol was then removed hy distillation until crystals beganto form in the reaction mixture. At this point a volume of toluene equalto the initial volume of methanol was added. The remainder of themethanol and the water in the reaction mixture were removed bydistillation. The toluene was then removed by I distillation atreducedpressure. A crystalline salt which was identified as (CeHo)sSlONawas obdered NaOH was added to [(CaHs)z(CHa)Sl1zO in amount to give asilicon to sodium ratio cl 1. The

till

equiv/a Fill) Fill reaction mixture was maintained at to C. for 2 hoursand at 120 to 130 C. for 2 hours. The water formed in the reaction wasremoved at reduced pressure. The reactionproduct was recrystallized froma mixed solvent composed of toluene and petroleum ether, boiling range-100 C. The recrystallized product was dehydrated at C. and 15 mm. Thesalt was identified as (CsHs)2(CHs)BlONa. The neutralization equivalentof the salt was 247. The calculated neutralization equivalent for theanhydrous salt is 236 (CcHs) (CI-lshSiONa was prepared by thereaction ofNaOH with [(CeHsliCI-BMBilzO. NaOI-I was added to wells) (CHaMSlJeO in areaction vessel in amount to give a silicon to sodium ratio of 1. warmedto 100 0., and small amounts of anhydrous methanol were added until asingle phase mixture was obtained. The methanol was then removed bydistillation. The reaction mixture was heated at C. atreduced pressurefor 3 hours to remove the water formed in the reaction. Upon cooling acrystalline mass was obtained. The crystals were recrystallized frompetroleum ether. boiling range 90-100 C., and identified as (CsHs)(CI-IsnSlONa. The neutralization equivalent of the salt was 181. Thecalculated neutralization equivalent oi the anhydrous salt is 174.

The three described salts were added with stirring to octamethylcyclotetrasiloxane in reaction vessels in amount to give a silicon tosodium ratio of 200. The reaction mixtures were maintained at atemperature of 100 C. Samples were tahen as in Example 1, and thefollowing results were obtained:

Enamzele 5 The reaction mixture was herons, prepared as in. mple 5. was

added to l a mixture of octamethylcyclotetrasiioxane and1,2,3,4-tetramethyl, 1,2,3,4-tetraphenyl cyclic tetrasiloxane at 118 C.in equimolar proportions in amount to give a silicon to sodium atomicratio of 965. The temperature was maintained at 118 C. for 96 hours andat 170 C.

for 120 hours. Samples of the reaction mixture were taken and the percent of cyclic siloxane polymerized determined by the per cent residueafter 3 hours at 250 C.260 C. and 1 micron pressure. The followingresults were obtained:

That which is claimed is:

1. The method of polymerizing cyclic diorganosiloxane to highermolecular weight polymers which comprises reacting at least one cyclicdiorganosiloxane selected'from the group consisting of dialkylsiloxanesand alkylarylsiloxanes with an alkali metal salt of a triorgano silanoluntil polymerization of the cyclic slloxane is effected, 1

2. The method of polymerizingcyclicdiorganosiloxane to higher molecularweight polymers which comprises reacting at least one cyclicdiorganosiloxane selected from the group consisting of dialkylsiloxanesand alkylarylsiloxanes with an alkali metal salt of a triorgano silanol,in amount less than one atom of alkali metal per 25 atoms of silicon,until polymerizationof the cyclic siloxane is effected.

3. The method of polymerizing cyclic diorgan osiloxane to highermolecular weight polymers which comprises reacting at least one cyclicdiorganosiloxane selected from the group consisting of dialkylsiloxanesand alkylarylsiloxanes, said cyclic diorganosiloxanes containing lessthan 12 silicon atoms per molecule with an alkali metal salt of atriorgano silanol, in amount less than one atom of alkali per 25 atomsof silicon, until polymerization of the cyclic siloxane is efiected.

, methylsiianol in amount less than one atom of 4. The method ofpolymerizing cyclic diorganosiloxane to higher molecular weightpolymerswhich comprises reacting at least on cyclic diorganosiloxane selectedfrom the group consist-t ing of dialkylsiloxanes and alkylarylsiloxanes,said cyclic dlorganosiloxanes containing less than 12 silicon atoms permolecule, with an alkali metal salt of a triorgano silanol, in amountless than one atom of alkali per 25 atoms of silicon, and maintainingreaction mixture formed at a temperature below the temperature at whichdestructive distillation would occur until polymerization of the cyclicsiloxane is efiected.

5. The method of polymerizing cyclic diorganosiloxane to highermolecular weight polymers which comprises reacting at least one cyclicdiorganosiloxane selected from the group consisting of dialkylsiloxanesand alkylarylsiloxanes. said cyclic diorgancsiloxanes containing lessthan 12 silicon atoms per molecule with an alkali metal salt of atriorgano silanol. in amount less than one atom of alkali per 25 atomsof silicon, in which cyclic siloxaneand silanol salt the organicradicals are bonded to the silicon by carbon to silicon bonding, and ata temperature below the temperature at which destructive distillationwould occur until polymerization of the cyclic siloxane is effected.

6. The method of polymerizing hexamethylcyclotrisiloxane to a highermolecular weight polymer which comprises reactinghexamethylcyclotrisiloxane with the potassium salt of tripotassium per50 atoms of silicon.

7; The method of polymerizing octamethyicyclotetrasiloxane to a highermolecular weight polymer which comprises reacting octamethyh- Noreferences cited.

